Parts of earth moving machinery and related equipment are subject to significant wear during use, principally due to abrasion. In an attempt to reduce the effects of this abrasion, wear components are often mounted to earth moving buckets and similar machinery. Typical wear components include heel shrouds, wear bars, corner shrouds and wing shrouds. These components are replaceable units, arranged to wear during use while protecting the bucket, and to be replaced before wearing completely through to the bucket.
It is desirable to make wear components from abrasion resistant materials, in order to extend their working life and to provide an enhanced benefit. It is also necessary to use materials which can withstand substantial impact forces, and the resulting stresses within the material. In general, it has been found that materials with high resistance to abrasive wear, such as chromium white irons and tungsten carbide composites, are generally too brittle to withstand the impact forces to which the heel shrouds are frequently subjected.
Additional difficulties have been experienced in successfully attaching components made of these materials to earth moving equipment. The materials are generally incapable of being welded, and the provision of holes and the like in the component for mechanical attachment can lead to unacceptable stress concentrations within the material.
As a result, most wear members are made from quenched and tempered steel, as this provides excellent strength properties along with a degree of resistance to abrasion.
An alternative type wear member has been proposed in the applicant's pending US patent application publication number US-2010-0275473-A1, the contents of which are incorporated herein by reference. This wear member comprises an outer shell of a tough metal such as a carbon steel, and an inner shell of an abrasion resistant metal such as a white iron.
This wear member has proved in testing to have many of the stated advantages. Nonetheless, it is considered desirable to provide a wear member having even greater strength than that of US-2010-0275473-A1.
It has also been observed that the use of an abrasion resistant material within an outer shell can significantly alter the wear rates of different parts of the wear member. It is considered desirable to take advantage of this observation in order to reduce the cost and weight of a wear member without substantially reducing its effectiveness. It is also considered desirable to provide a means of easily determining when a wear member has reached the end of its useful life.
Different aspects of the present invention seek to achieve these desiderata.